1. Field of the Invention
The present invention relates to an excimer laser device in which gas for excimer laser is sealed in a chamber, pulse oscillation is carried out in the chamber to excite the gas for the excimer laser so to oscillate the pulsed laser, and gas for excimer laser, and more particularly to an excimer laser device which improves a burst phenomenon and a spiking phenomenon of a laser output by adding xenon gas, and gas for excimer laser.
2. Description of the Related Art
Conventionally, a semiconductor exposure device provided with an excimer laser device as a light source alternately repeats the exposure and the movement of the stage to expose an IC chip on a semiconductor wafer to light, so that the excimer laser device performs a burst operation which repeats a continuous pulse oscillating operation for continuously oscillating a pulse of laser light for a predetermined number of times and a suspension of oscillation for suspending the pulse oscillation for a predetermined duration.
FIG. 6(a) is a diagram showing a relation between energy and a burst number when the burst operation is performed by a conventional excimer laser device. It is seen that the burst operation of the excimer laser device has a characteristic (hereinafter called the burst characteristic) that energy is high at first and lowers gradually.
FIG. 6(b) is a diagram showing a relation between a pulse and energy at each burst. It is seen that the continuous pulse oscillating operation has a characteristic (hereinafter called the spike characteristic) that energy is relatively high at the beginning and then pulse energy lowers gradually.
Thus, when the existing excimer laser device is used to perform the burst operation, the burst characteristic and the spike characteristic are demonstrated generally.
But, the occurrence of the burst characteristic in the laser output by the excimer laser device had a drawback of causing variations in an amount of light exposure due to variations in energy at each burst.
There was also a drawback that when the spike characteristic was caused in the laser output, accuracy of the amount of light exposure was further lowered, so that it was necessary to make complex discharge voltage control.
Specifically, the discharging voltage was conventionally changed for each pulse by lowering the discharging voltage (charging voltage) of the initial pulse of the continuous pulse oscillation in the burst mode and gradually increasing the following discharging voltage of the pulse, thereby preventing the initial energy increase due to the spiking phenomenon. Therefore, complex control of the discharging voltage was necessary.
Thus, in performing the burst operation of the excimer laser device, it was a very significant issue to efficiently remedy the burst characteristic and the spike characteristic of the laser output.
“Transmission Properties of Spark Preionization Radiation in Rare-Gas Halide Laser Gas Mixes” disclosed in “IEEE JOURNAL OF ELECTRONICS, VOL. 31, No. 12, December 1995, p2195–p2207” suggests a technology of adding xenon gas to neon gas alone. But, this conventional technology is a technology just to increase the spark preionization but not to remedy the burst characteristic and the spike characteristic of the excimer laser output.